1. Field of the Invention
The present invention relates to a read head that has a read track width defining layer that planarizes the write gap layer of a write head and, more particularly, to a read head and method of making wherein a read track width defining layer is located between the read sensor of the read head and the write gap layer of the write head and has a thickness which substantially planarizes the read head at the level of first and second hard bias and lead layers which, by replication of subsequent layers, planarizes the write gap layer.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A write gap layer between the first and second pole piece layers forms a magnetic gap at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the magnetic gap between the pole pieces. This field fringes across the magnetic gap for the purpose of writing information in tracks on moving media, such as the circular tracks on the aforementioned rotating disk, or a linearly moving magnetic tape in a tape drive.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor for conducting a sense current through the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. The read sensor has first and second side edges that define a track width of the read head. The product of the linear density and the track density equals the real density of the read head which is the bit reading capability of the read head per square inch of the magnetic media.
Rows and columns of combined read and write heads are made on a wafer substrate located in various chambers where layers are deposited and then defined by subtractive processes. A plurality of substrate wafers may be located on a turntable which rotates within the chamber and which may function as an anode. One or more targets, which comprise materials that are to be deposited on the wafer substrates, may also be located in the chamber. The target functions as a cathode and a DC or RF bias may be applied to the cathode and/or the anode. The chamber contains a gas, typically argon (Ar), which is under a predetermined pressure. Material is then sputtered from a target onto the wafer substrates forming a layer of the desired material. Layers may also be deposited by ion beam deposition wherein an ion beam gun directs ionized atoms (ions) onto a target which causes the target to sputter material on the wafer substrate. A subtractive process may employ a gas in the chamber, such as argon (Ar), under pressure which causes sputtering of the material from portions of the wafer substrate not covered by a mask. Alternatively, the subtractive process may employ an ion beam gun that discharges high velocity ions, such as argon (Ar) ions, which impact and remove portions of the wafer substrate that are not covered by a mask.
First and second hard bias and lead layers are typically joined at first and second side edges of the read sensor in what is known in the art as a contiguous junction. A first step in making this junction is forming a read sensor material layer over the entire wafer. Then, for each magnetic head a bilayer photoresist is formed over the desired read sensor site with a top layer portion that has first and second side edges for defining the first and second side edges of the read sensor and a bottom layer portion directly on the read sensor material layer that is recessed from the top layer portion so as to provide undercuts for the purpose of lifting off subsequently deposited unwanted layer portions. The wafer is then rotated by the turntable and a subtractive process, such as ion milling, is employed for removing all of the read sensor material layer except the read sensor under the bilayer photoresist. Unfortunately, the read sensors on the outside of the wafer are subjected to a different ion milling angle than wafers on the inside of the wafer, resulting in magnetic heads which have different characteristics. A first side edge of the read sensors on the outside of the wafer is notched while a second side edge is not notched. This is due to the fact that the turntable is rotated about an axis that is at an angle to the milling direction for the purpose of minimizing redeposition of the milled material. While the bilayer photoresist is still in place a hard bias and lead layer material is deposited on the entire wafer substrate. The bilayer photoresist is then removed lifting off the bias and lead layer material deposited thereon. The result is that a first hard bias and lead layer makes good abutting engagement with the first side edge of the read sensor, however, the second hard bias and lead layer may make only partial abutting engagement with the notched second side edge of the read sensor. This occurs because the angle of deposition of the hard bias and lead layer material is different than the angle of ion milling of the second side of the read sensor. The result is that the hard bias material adjacent the notched side edge may not make sufficient abutting contact for magnetically stabilizing the magnetic domains of the read sensor. This would degrade the performance of the read head.
Another problem is that the undercut of the bilayer photoresist permits ion milling to mill, to some extent, under the undercut. This results in an unpredictable track width of the read sensor.
A further problem noted with the above process is that upon deposition of the hard bias and lead layer material there is some overlap of the hard bias and/or lead layer material on a top surface portion of the read sensor adjacent each of the first and second side edges. This can cause an exchange coupling between the hard bias material and the read sensor which adversely affects the magnetics of the read sensor and may alter the expected track width of the read sensor.
Still another problem with the above process is that the first and second hard bias and lead layers have a higher profile than the read sensor. When the second gap, the second shield/first pole piece layer and the write gap layer of the write head are deposited there is a dip in the gap layer. This dip is known in the art as write gap curvature and can significantly degrade the performance of the write head. With a curved write gap the write head writes curved magnetic impressions into a rotating disk which are then read by a linearly extending read sensor. The read sensor will only read the center portion of the curved impression which reduces read signal performance.
The present invention provides a read and write head combination wherein the read head is planarized so as to overcome write gap curvature. A method of making is also provided where a read track width defining layer is employed for defining the track width of the read sensor with improved side edges. In a preferred embodiment the read track width defining layer remains in the head for planarizing the read head and overcoming the write gap curvature problem.
In the method a read track width defining material layer is formed on a read sensor material layer. The bilayer photoresist mask is then formed for masking the aforementioned read track width defining layer. A first selective removing process is then employed for removing the read track width defining material layer, except for the read track width defining layer that is masked by the photoresist mask. The first selective removing forms the read track width defining layer with exposed first and second side edges. Then a second selective removing process is employed for removing the read sensor material layer, except for a read sensor layer portion masked by the read track width defining layer. The second selective removing process forms a read sensor layer with exposed first and second side edges. Then, hard bias and lead material layers are deposited on the photoresist mask adjacent the first and second side edges of each of the read sensor layer and the read track width defining layer. Finally, the photoresist mask is removed thereby lifting off a portion of the hard bias and lead material layer leaving first and second hard bias and lead layers connected to the first and second side edges of each of the read sensor layer and the read track width defining layer.
In a preferred embodiment the track width defining layer is carbon. When the read track width defining layer is carbon the first selective removing is preferably a reactive ion etch with an oxygen (O2) base. Other materials for the read track width defining layer may be silicon (Si) or silicon dioxide (SiO2). When the read track width defining layer is silicon (Si) or silicon dioxide (SiO2) the first selective removing process may be a reactive ion etch with a freon (CF4) base. In the preferred embodiment the read track width defining layer has a thickness which is the difference between the thickness of the hard bias and lead layer and the thickness of the read sensor. With this arrangement the read track width defining layer planarizes the read head at the hard bias and lead layer level so that subsequent layers formed on the read sensor and the first and second hard bias and lead layers do not replicate a curvature to the write gap of the write head. If desired, however, the read track width defining layer may be removed by ashing in the presence of oxygen (O2) within a chamber.
An object of the present invention is to provide a combined read and write head wherein the read head is planarized so as to obviate write gap curvature of the write head.
Another object of the present invention is to provide a read head wherein contiguous junctions are made between first and second hard bias and lead layers and first and second side edges of a read sensor respectively wherein the first and second hard bias and lead layers do not overlap first and second surface portions adjacent the first and second side edges of the read sensor.
A further object of the present invention is to provide a read and write head wherein each of first and second hard bias and lead layers make a continuous abutting junction with precisely located first and second side edges of the read sensor.
Still another object is to provide a method of making a read and write magnetic head wherein a bilayer photoresist mask is employed for defining a read track width defining layer which, in turn, is employed for defining the read track width of a read sensor.
Still a further object is to provide a method of making a read and write magnetic head which substantially eliminates any portion of first and second hard bias and lead layers covering a top surface of the read sensor, implements complete abutting engagement of the first and second hard bias and lead layers with first and second side edges of the read sensor and planarizes the read head so that no curvature is replicated to the write gap layer of the write head.